Mining machine having cutter arms oscillated in opposite directions and in phase



1967 B. FRELLSEN 3,333,894

C. MINING MACHINE HAVING CUTTER ARMS OSCILLATED IN OPPOSITE DIRECTIONS AND IN PHASE Flled Sept. 28, 1964 2 Sheets-Sheet 2 FIg.3.

7o 94 92 I56 I60 68 72 ,soI64I32 l84|3276 7a 90 96 a2 $3152 I34 74 IssIzs 24 8 H I05 H6 II2 -2o2 2Io [200 208 INVENTOR. I92 I98 CARLTON B.FRELLSEN BY 18 6M w I90 I94 I96 hisvATIORNEY United States Patent MINING MACHINE HAVING CUTTER ARMS OSCILLATED IN OPPOSITE DIRECTIONS AND IN PHASE Carlton B. Frellsen, Franklin, Pa., assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 28, 1964, Ser. No. 399,684 11 Claims. (Cl. 2991) This invention relates to a continuous mining apparatus having a pair of mineral disintegrating or cutter heads and more particularly to a new and improved means for oscillating the cutter heads in opposite directions and in phase.

In the design of continuous miners having a pair of reciprocable cutter heads, it has been known to employ a mechanism for oscillating the cutter heads in a horizontal direction. Such apparatus utilized a common mechanical driving means for both actuating the cutter heads and for oscillating the cutter heads.

Although such devices have served the purpose, they have not been entirely satisfactory under all conditions of operation because oscillation of the cutter heads is dependent upon the cutter drive mechanism. Accordingly, oscillation cannot be stopped at any intermediate position without stopping the cutter drive. Furthermore, in the event one cutter head stalled due to its encounter with a strong resistance such as rock mineral for example, the excessive strains and forces transmitted to the oscillating mechanical drive mechanism resulted in the fracture and breakage of parts.

The general purpose of this invention is to provide a new and improved oscillating means, independent of the cutter drive mechanism, for oscillating the cutter heads of a continuous miner in opposite directions and in phase.

Accordingly, it is an object of the present invention to provide a new and improved continuous mining machine.

Another object of this invention is to provide a new and improved continuou mining machine having novel means for oscillating the cutter heads at a uniform rate in opposite directions and in phase.

It is a further object of the present invention to provide a new and improved continuous mining machine having hydraulic means, independent of the cutter drive mechanism, for oscillating a pair of cutter heads so that oscillation of the cutter heads may be halted at any selected transverse position without terminating the cutting operation.

It is a specific object of the present invention to provide a new and improved continuous mining machine having means for oscillating -a pair of cutter heads through a given stroke, said means including means to permit the direction of said oscillating movement to be reversed before the completion of said given stroke.

It is another specific object of this invention to provide a new and improved continuous mining machine having means for oscillating a pair of cutter heads, said means including means to stall one cutter head in the event the other cutter head stalls.

These and other objects of the present invention will become more apparent when taken in conjunction with the following detailed description and drawings in which:

FIG. 1 is a partial fragmentary top plan view of the continuous mining machine constructed in accordance with the principles of the present invention with a portion of the cover plate broken away to show the mounting of the actuating cylinders and connecting rods with respect to the oscillating arms;

FIG. 2 is an enlarged fragmentary view showing the crank drive assembly for the oscillating means;

3,333,894 Patented Aug. 1, 1967 FIG. 3 is an enlarged central sectional view, taken on the plane of the line 33 of FIGURE 1, through the servo v-alve mechanism showing the valve in neutral position; and

FIG. 4 is a diagrammatic view illustrating the hydraulic circuit for the oscillating means.

The improved continuous mining machine, as shown in the drawings, constitutes an improvement of application Ser. No. 399,178, filed Sept. 25, 1964, which application is assigned to the same assignee as the instant application. For a more detailed description of the general arrangement of the continuous miner of the present invention, as for example, the mobile base frame, the boom frame, the conveyor, the gathering head, etc. see copending application Ser. No. 399,178 above referred to. The description of the present invention will be restricted substantially to the novel means for oscillating the cutter heads.

With reference to FIGURE 1, it will be seen that a pivotable boom frame generally designated 10 contains a pair of oscillating arms generally designated 12, each arm comprising an elongated hollow tubular member 14 having a cutter head or gear case housing 16 disposed at the forward end (upper portion of machine as viewed in FIG. 1) thereof for enclosing a suitable cutter drive mechanism (not shown) for rotating a plurality of suitable rotary cutter discs adapted to be mounted on said cutter heads 16 in a manner similar to that disclosed in the copending application Ser. No. 399,178.

A front plate 20 is rigidly secured, as by means of welding for example, onto a bottom cover plate 22 of the boom frame shrouding. A pair of suitable plates 24 extend laterally inwardly from housings 16 and are movable therewith respectively, and cooperate wit-h front plate 20 to form a front face of the shrouding so that the oscillation controls and cutter drive mechanism may be protected in any lateral disposition of oscillating arms 12.

A pair of actuating double acting hydraulic cylinders 26, 26a are provided adjacent the forward central portion of the boom frame for oscillating the arms 12 in a horizontal direction, each cylinder being connected between the boom frame 10 and oscillating arm 12. Cylinders 26, 26a comprise elongated cylindrical casings 28, 28a pivotably mounted at their outer sides at 30, 30a, respectively, to brackets 32, 32a secured to the inner sides of housings 16 of oscillating arms 12 respectively. These cylinders contain pistons (not shown) having laterally and inwardly extending piston rods 34, 34a pivotably connected at 36, 36a, respectively, to brackets 38, 38a, respectively, which are secured to front plate 20.

A conventional hydraulic motor 40 is suitably rigidly secured to a bracket 42 of the boom frame in any manner well known in the art and drives a splined shaft 44 (FIGURE 2). A sprocket 46 is suitably matingly splined to shaft 44 for engaging and driving an endless chain 48 which in turn drives an idler sprocket 50. Sprocket 50 is rigidly secured to a double ended crankshaft 52, each end of said shaft having a crank arm 54 suitably rigidly secured thereto as by means of a key 53 as shown in FIGURE 2.

Extending substantially transversely from the inner sides of the oscillating arms are a pair of connecting rods generally designated 56, 56a (FIG. 1) disposed from each other and having at their one ends respectively, rod end links 58, 58a pivotally connected to the crank arms as at 59, 59a, and having at their other ends respectively, rod ends 60, 60a pivotably connected to brackets 64, 64a respectively, as at 62, 62a, said brackets being rigidly secured to oscillating arms 12. Servo valves 66, 66a are releasably secured intermediate the ends of the connecting rods, respectively, in such manner that the distance between the pivot points is adjustable.

Since servo valves 66, 66a are identical in structure and function, the description will be confined to servo valve 66 (FIG. 3). The valve comprises a cylindrical housing generally designated 68 consisting of a left end cap portion 70 (the directions being taken as seen in FIGURE 3), a retaining plate 72, an intermediate portion 74, a retaining plate 76 and a right end head portion 78, all suitably rigidly secured together as by means of four hex head cap screws 80 (only two of which are shown in FIGURE 3) which are threaded into cooperating bores 82 respectively. A retainer ring 79 is threadedly secured within the cap portion 70 of housing 68.

Extending axially outwardly from the retainer ring 79 and slidable relative thereto is an elongated metallic rod member 84 having a threaded portion 86 for adjustably accommodating the rod end link 58 of the connecting rod. Rod member 84 has a reduced cylindrical portion 88 about which are disposed a pair of circular metallic spaced discs 90 and 92 in bore 91 of cap portion 70 for retaining a spring 94 therebetwen. Disc 92 abuts shoulder 96 of cap portion 70 and a smaller circular metallic disc 98 which is disposed about a further reduced cylindrical portion 100 of the rod member 84, said smaller disc abutting a hex nut 102 threadedly secured onto the mated threaded end portion 104 of rod member 84.

Normally, the preloaded spring 94 will remain in its expanded condition, so that movement of rod 84 to the right as viewed in FIGURE 3 for example, will effect movement of the entire housing in the same direction via disc 90, spring 94, disc 92 and shoulder 96 while movement of rod 84 to the left will effect a corresponding movement of the housing in the same direction via nut 102, disc 98, disc 92, spring 94 and disc 90. Spring 94 has the double function of absorbing unusual shocks and impacts of a relative high force to preclude strain and fatigue on the fixed abutting elements of the servo valve and to aid in reversing the servo valve in the event an oscillating arm is stalled near the end of its stroke as will hereinafter be more fully explained.

Turning now to the other end of servo valve 66, it will be noted that a sleeve 106 is slidably mounted within a bore 105 of the head end 78 of housing 68 and is internally threaded as at 108 to adjustably receive the externally threaded portion 110 of rod end 60 of the connecting rod. Sleeve 106 is diametrically slotted as at 112 and 114 to permit the sleeve to be radially compressed for locking rod end 60 within the sleeve by means of a suitable clamping member 116.

Sleeve 106 has an annular flange 118 extending radially inwardly, said flange having spaced surfaces 120 and 122. Surface 120 abuttingly engages the right end face 124 of a spool valve 126 and surface 122 engages the shoulder or flange portion of a bushing 128, which in turn abuttingly engages the hex head cap 130 of an elongated cap screw 132. Bushing 128 fits loosely into sleeve 106 in order to take the weight ofl? spool valve 126. The weight of the valve proper is carried by the cylindrical surface of sleeve 106 bearing on head portion 78 and the cylindrical surface of rod 84 bearing on retainer ring 79. This limits the forces acting on the spool valve to axial forces of push or pull.

A bore 134 is provided in housing 68 for slidably containing the spool valve 126. This spool valve has a reduced diameter stem portion 136 at its left end whereby an annular shoulder 138 is formed by the transition between the full diameter of the spool valve and the reduced diameter stem portion thereof.

The left end face 140 of the spool valve abuts a circular metallic disc 142 which in turn abuts a hex nut 144 threadedly secured onto the externally threaded end portion 146 of cap screw 132. The spool valve and cap screw are so interconnected as to act as a unitary structure and are movable together.

Bore 134 is counterbored as at 148 for receiving a pair of annular spring abutment guide members 150 and 152.

A spring 154 extends between shoulders or flanges 156 and 158 of abutment members and 152 respectively. Spring abutment member 150 has an annular radially inwardly extending shoulder or flange 160 which abuttingly engages circular disc 142 while spring abutment member 152 has an annular radially inwardly extending flange or shoulder 162 which abuttingly engages shoulder 138 of spool valve 126. The distance between flanges 160 and 162 of abutment members 150 and 152 respectively, establishes the amount of travel that the spool valve can move relative to housing 68 from its neutral or centered position as seen in FIG. 3. Spring 154 maintains the spool valve centered until a force is applied to either the spool valve or the housing.

The spool valve is provided adjacent the central portion thereof with two reduced diameter portions or annular recesses 164 and 166 respectively, which direct fluid flow through housing 68 and are alternatively connected to pressure and exhaust.

Bore 134 of housing 68 is provided with five annular enlargements or groves 168, 170, 172, 174 and 176 respectively. Groove 168 is connected by passage 178 to groove 176 which in turn is connected to exhaust via port 180. Grooves and 174 are connected to ports 182 and 184 respectively which lead to the rod end and head end respectively, of cylinder 26. Groove 172 is connected to pressure via port 186.

Referring now to the diagrammatic showing of the hydraulic circuit in FIGURE 4, it will be observed that a source of hydraulic fluid is shown at 188 as, for example, a suitably disposed tank or receptacle to contain the necessary quantity of hydraulic fluid. The source 188 is connected by a suitable suction line 190 with a suitable pump 192 which is driven from any suitable source of power, not shown. The source of power employed to drive pump 19 2 is separate from that which powers the rotary cutters.

Pump 192 delivers fluid under pressure to a line 194 which is connected with the main hydraulic control valve 196. Leading from the control valve is a conduit 198 connected to a suitable pressure reducing valve 200 which in turn is connected by means of a conduit 202 to bydraulic motor 40. Motor 40 is connected to a conduit 204 which leads back to the source 188 by means of return conduit 206.

Also leading from the control valve 196 is a conduit 208 connected to a conventional flow divider 210 which assures equal volume to conduits 212 and 214, which connect the flow divider to suitable relief valves 216 and 218 respectively, which in turn are connected by conduits 220 and 222 respectively, to the pressure port 186 of servo valves 66 and 6611 respectively. Conduits 219 and 219' connect relief valves 216 and 218 respectively to the source 188 by means of return conduit 206. Servo valves 66 and 66a are connected with suitable conduits 224 and 226 respectively, which lead back to the source 188 by way of return conduit 206. Conduits 228 and 230 connect servo valve 66 with the head end and rod end respectively, of actuating cylinder 26. Conduits 232 and 234 connect servo valve 66a with the head end and rod end respectively, of actuating cylinder 26a.

Operation of the mining machine of the present invention is the same as that described for the hereinbefore cited copending application, excepting only that the cutter heads are oscillated by a new and improved hydraulic means. It should be noted that oscillation of the cutter heads may be selectively started or terminated at any time during the cutting operation and that the oscillation means is controlled by an independent hydraulic circuit. The speed of oscillation is determined by the quantity of oil supplied to the actuating cylinders.

Because both servo valves operate in the same manner at precisely apart, the mode of operation will be restricted to servo valve 66 alone, the operation thereof being as follows: hydraulic fluid under suitably reduced pressure, as for example 500 p.s.i., is applied to hydraulic motor 40 causing it to turn the crank rod 54 in a clockwise direction by means of the crank drive assembly illustrated in FIGURE 2, while hydraulic fluid under a re1atively higher pressure, as for example 2000 p.s.i., is simultaneously applied to the pressure port 180 of servo valve 66. While the above relative pressures are preferable, it should be appreciated that other pressures and presssure ratios are envisaged without departing from the spirit of the present invention.

Assume that cutter heads 18 are located in their most laterally inwardly retracted position, a condition which would orient the crank arms 54 in a horizontal position or 90 prior to reaching the vertical position as seen in FIGURE 4. Rotation of crank arms 54 in a clockwise direction effects movement of rod 58 to the right as viewed in FIGURE 4, carrying along with it housing 68 relative to spool valve 126 by means of rod member 84, disc 90, spring 94, disc 92 and shoulder 96. The force is great enough to overcome the bias of spring 154 and abutment member 150 will move linearly relative to member 152, such relative motion being limited by the distance between the two abutment members. Such movement seals oft recess 164 from pressure and establishes pressure fluid flow through port 186, recess 166, groove 174, port 184, conduit 228 to the head end of cylinder 26 causing it to move the oscillating arm 12 to the right as seen in FIGURE 4. Fluid from the rod end of cylinder 26 is exhausted through conduit 230, port 182, recess 164, groove 168, passage 178, port 180, conduit 224 to tank.

Movement of arm 12 outwardly carries along with it spool valve 126 by means of member 60, sleeve 106, bushing 128, cap screw 132, nut 144 and disc 142. It will thus be seen that the spool valve attempts to center itself relative to housing 68 and establish a neutral position as shown in FIGURE 3, but due to the continuous motion applied to housing 68 by rotation of the crank, such a condition will not exist except when the opposite arm is stalled or when the crank drive hydraulic motor is stopped. When the connecting rod reaches the end of its throw, the hydraulic motor will rapidly accelerate (hereinafter more fully explained) and effect a quick reversal of the valve. When the connecting rod reverses direction, it moves housing 68 leftwardly relative to the spool valve, thus reversing the pressure to the cylinder and reversing the movement of arm 12. Specifically, movement of rod 84 leftwardly (FIGURE 3) moves housing 68 in the same direction by means of nut 102, disc 98, disc 92, spring 94 and disc 90. Pressure fluid flow is then established through pressure port 186, recess 164, groove 170, port 182, conduit 230 to the rod end of cylinder 26 while the head end of cylinder 26 is exhausted through conduit 228, port 184, groove 174, recess 166, groove 176, port 180, conduit 224 to tank. This cycle is repeated with eachrotation of the crank and continues as long as the hydraulic motor turns the crank.

Since the crank drive hydraulic motor is driven by the system pump and is designed to operate at lower than system pressure, it has access to a greater quantity of oil than it can use. When the pistons in the cylinders approach the end of the stroke, the valve actuating rods reach the end of their throw. At this point, the speed of the motor is not limited to the velocity of the oscillating arm and it accelerates rapidly through a small arc to effect a quick reversal of the valves whereupon it is again limited in speed by the velocity of the arm. This is repetitive at the end of each stroke. The throw of the arm determines the length of the cylinder stroke, the maximum being the full cylinder stroke.

It should be noted that the hydraulic motor 40 and its crankshaft do not have the power to actuate the oscillating arms; they only actuate the servo valves which in turn supply pressure fluid to the cylinders which provide the motive power for the oscillating arms.

The above described invention assures that oscillation of the cutter heads will move in opposite directions and in phase. It should be noted that the amplitude of oscillation is normally fixed and that the cutter heads will move substantially the same distance in every cycle. However, stalling either oscillating arm stops the hydraulic motor and, in turn, stops the other arm. By way of example, assume that one of the arms stalls midway in its stroke while oscillating laterally outwardly due to its encounter with a strong resistance large enough to overcome the pressure in the actuating cylinders. The associated spool valve 126 will stop and its housing 86 will stop when abutment member 150 engages member 152, such relative linear movement being on the order of 7 of an inch, for example. This in turn stalls the crank drive mechanism and hydraulic motor and the spool valve will continue to be held in the operative position. Accordingly, movement of the housing of the other servo valve will stop and its associated oscillating arm will advance only until it centers its spool valve relative to the housing, effecting a neutral position thereof, causing its associated oscillating arm to stall. Thus, the two oscillating arms will not be thrown out of phase and no undue strain or damage to the mechanical elements will occur. Pressure will continue to be applied to the first stalled arm, and as soon as it becomes free, oscillation will be re-established.

Now assume that the oscillating arm stalls near the completion of its outward stroke, for example, within 10% of reaching its outward limit. Because the longitudinal axes of the rod 58 and crank arm 54 are approaching coincidence, that is, Within the last 18 of rotation of crank arm 54 before end of throw, the forces exerted are sufiicient to collapse spring 94 by means of rod 58, member 84 and disc 90. Accordingly, rod 58 moves relative to housing 68 a small linear distance and reaches the end of its throw whereat it is quickly reversed to effect reversal of the oscillating arm. Thus, if the arm stalls near the completion of its stroke, it will be reversed without having to complete said stroke. This occurs only when the arm stalls near the end limits of its stroke.

In the event the external force is so great as to force an arm inwardly, for example if the arm engages rock strata while turning a corner during tramming, pressure will be relieved via conduit 228, port 184, recess 166, port 186, conduit 220 through the relief valve 216. Since movement of spool valve leftwardly (FIG. 3) relative to housing 68 will increase, spring abutment member 152 engages spring abutment member 150, forcing the housing and its associated rod member leftwardly, thus reversing the rotation of the crankshaft. Accordingly, the other servo valve will effect a corresponding inward movement of its associated arm, thus keeping the arms in phase and in step. When the obstruction is removed, the arms will again move outwardly to complete their cycle. It should be appreciated that the same results are obtained if stalling occurs during inward movement of the arms.

As a result of this invention, an improved continuous mining machine of the oscillating cutter head type is provided for dislod-ging and disintegrating the mineral of a solid mine vein in an improved and more efficient man ner.

The improved continuous mining machine of this invention is not only eflicient and reliable in operation, but is also simple and rugged in design, well adapted to meet the severe conditions of service encountered in a mine.

Another advantage residing in the apparatus of this invention is that oscillation of the cutter heads is independent of the cutter drive means so that oscillation can be halted without terminating the cutting operation. For example, oscillation can be stopped at the maximum Width of the cutter heads for rib slabbing or turning crosscuts; or at any intermediate position for traveling or cutting large lumps from roof falls.

A further advantage residing in the apparatus of this invention is that means are provided for oscillating a pair of cutter heads through a given stroke, said means including means to permit the direction of movement of said heads to be reversed before the completion of said given stroke.

A preferred embodiment of the principles of this invention having been hereinabove described and illustrated, it is to be realized that modifications thereof can be made without departing from the broad spirit and scope of this invention as defined in the appended claims.

I claim:

1. In a mining apparatus having a mobile frame; a pair of forwardly extending elongated support arms mounted at one end thereof on said mobile frame for pivotal movement about spaced axes respectively; cutting means carried at the other ends of each of said support arms; double acting hydraulic cylinder means having a pressurizable head portion and a pressurizable rod portion for each of said support arms, respectively, said cylinder means mechanically connecting said arms and said frame, respectively; a hydraulic circuit having a fluid pumping portion and a fluid returning portion for alternately pressurizing said head portions and said rod portions to oscillate said support arms through a given cycle about said axes in opposite directions, respectively; valve means for directing fluid flow to and from said cylinder portions, individually; and control means operating said valve means in response to a decrease in the oscillation rate of one of said support arms for establishing communication of said cylinder head and rod portions, associated with the other of said arms, with said pumping and returning portions of said circuit.

2. The mining apparatus as specified in claim 1 wherein said control means operates said valve means to throttle the delivery of pressure fluid to the cylinder portions associated with said other arm in response to a decrease in the oscillation rate of said one arm.

3. The mining apparatus as specified in claim 1 wherein said hydraulic cylinder means comprises a pair of double acting hydraulic cylinders and said valve means comprises a pair of servo valves communicating with said cylinders, respectively, said Servo valves having first and second movable members, respectively, said first movable members being connected to said arms, respectively, and said second movable members being movable by said control means.

4. In a mining apparatus having a mobile frame; a pair of forwardly extending elongated support arms mounted at one end thereof on said mobile frame for pivotal movement about spaced axes respectively; cutting means carried at the other end of each of said support arms; a pair of double acting hydraulic cylinders connected between said mobile frame and said support arms, respectively, each of said cylinders having a pressurizable head portion and a pressurizable rod portion; a hydraulic circuit having a fluid pumping portion and a fluid returning portion for pressurizing said head portions and said rod portions to cyclically oscillate said support arms about said axes in opposite directions, respectively, from one extreme position to an opposite extreme position for each of said arms; a pair of valves having relatively movable members for directing fluid flow to and from said cylinder portions, individually; and control means connected to, and operating some of said movable members for hydraulically synchronizing the oscillations of said support arms, said control means also operating said movable members at either of said extreme positions to momentarily connect the head portions and rod portions of both cylinders to the returning portion of said circuit.

5. The mining apparatus as specified in claim 4 wherein said valves are servo valves, said movable members are first and second movable members in each valve, said first members being connected to said arms and movable therewith, said second members being connected to said control means and movable thereby and said control means also operates said second movable members in response to a decrease in the oscillation rate of one of said arms for establishing communication of the head and rod portions of the cylinder connected to the other of said arms with said pumping and returning portions of said circuit.

6. The mining apparatus as specified in claim 5 wherein said fluid pumping portion of said hydraulic circuit comprises flow dividing means providing equal volume flow to two subportions of said pumping portion communicating individually with said pair of cylinders throughout a range of pressures on the two subportions as determined by resistance to the movement of the respective arms and cutting means.

7. In a mining apparatus having a mobile frame; a pair of forwardly extending elongated support arms mounted at one end thereof on said mobile frame for pivotal movement about spaced axes respectively; a cutter head rotatably mounted at the other end of each of said support arms, respectively; a double acting hydraulic cylinder connected between said mobile frame and each of said support arms for oscillating said support arms through a given cycle about said axes in opposite directions, respectively; a pair of servo valves mechanically connected to said support arms for regulating fluid flow through said cylinders, respectively, motor operated camming means rotatably mounted on said mobile frame external to said servo valves; adjustable linkage means connected between said camming means and said servo valves, respectively, to synchronize the oscillations of said support arms and to operate said servo valves in response to a decrease in the oscillation rate of one of said support arms to cause a like change in the oscillation rate of the other of said arms.

8. The mining apparatus as specified in claim 7 wherein said camming means comprises a pair of cranks oppositely oriented from the axis of crank rotation and said camming means are rotated by a variable speed motor connected thereto responsive to rotation resistance and reversible by a force applied to either of said arms great enough to overcome the rotative force of said motor.

9. The mining apparatus as specified in claim 8 wherein one movable member of each of said servo valves is connected to said linkage means by means yieldable through a distance great enough to allow up to 18 degrees of crank rotation prior to the end-of-throw position of said camming means without movement of the respective support arm.

10. In a mining apparatus having a mobile frame; a pair of forwardly extending elongated support arms mounted at one end thereof on said mobile frame for pivotal movements about spaced axes respectively; rotatable cutter heads mounted at the other ends of said support arms, respectively; a pair of double acting hydraulic cylinders connected between said mobile frame and said support arms, respectively, each of said cylinders having a pressurizable head portion and a pressurizable rod portion; a pressurizable hydraulic circuit having a fluid pumping portion and a fluid returning portion communicating with said cylinders for pressurizing said head portions and said rod portion to oscillate said support arms through a given cycle about said axes in opposite directions, respectively, between positions of motion reversal for each of said arms; a pair of servo valves in said hydraulic circuit for regulating fluid flow through said cylinders, respectively; each of said servo valves having first and second movable members, said first members being mechanically connected to said support arms; camming means rotatably mounted on said mobile frame; and linkage means connected between said camming means and said second members to operate said servo valves in response to a decrease in the oscillation rate of one of said support arms for establishing communication of the head and rod portions of the cylinder connected to the other of said arms with said pumping and returning portions of said circuit and also to operate said servo valves at any position of motion reversal to momentarily connect the head portions and rod portions of both cylinders to the returning portion of said circuit.

11. A mining apparatus comprising: a mobile frame; a boom frame mounted on said mobile frame for pivotal movement about an axis; a pair of elongated arms mounted on said boom frame for pivotal movement about spaced axes; a pair of cutter heads spaced from said spaced axes and supported by said arms, respectively; means for actuating said cutter heads; pressure fluid means mounted at least in part on said boom frame and independent of said actuating means for oscillating said pair of arms about said spaced axes in opposite directions, respectively; said pressure fluid means comprising a source of fluid pressure; a pair of actuating cylinders on said boom frame operatively connected to said arms, respectively; a crank drive mechanism mounted on said boom frame; means for References Cited UNITED STATES PATENTS 1,880,091 9/1932 Hughes 29971 X 2,590,014 3/1952 Ivanolf et al 9139 X 3,052,454 9/1962 Sibley 299-71 3,170,732 2/1965 Hlinsky 29971 3,302,974 2/1967 Hlinsky 2991 ERNEST R. PURSER, Primary Examiner. 

1. IN A MINING APPARATUS HAVING A MOBILE FRAME; A PAIR OF FORWARDLY EXTENDING ELONGATED SUPPORT ARMS MOUNTED AT ONE END THEREOF ON SAID MOBILE FRAME FOR PIVOTAL MOVEMENT ABOUT SPACED AXES RESPECTIVELY; CUTTING MEANS CARRIED AT THE OTHER ENDS OF EACH OF SAID SUPPORT ARMS; DOUBLE ACTING HYDRAULIC CYLINDER MEANS HAVING A PRESSURIZABLE HEAD PORTION AND A PRESSURIZABLE ROD PORTION FOR EACH OF SAID SUPPORT ARMS RESPECTIVELY, SAID CYLINDER MEANS MECHANICALLY CONNECTING SAID ARMS AND SAID FRAME, RESPECTIVELY; A HYDRAULIC CIRCUIT HAVING A FLUID PUMPING PORTION AND A FLUID RETURNING PORTION FOR ALTERNATELY PRESSURIZING SAID HEAD PORTIONS AND SAID ROD PORTIONS TO OSCILLATE SAID SUPPORT ARMS THROUGH A GIVEN CYCLE ABOUT SAID AXES IN OPPOSITE DIRECTIONS, RESPECTIVELY; VALVE MEANS FOR DIRECTING FLUID FLOW TO AND FROM SAID CYLINDER PORTIONS, INDIVIDUALLY; AND CONTROL MEANS OPERATING SAID VALVE MEANS IN RESPONSE TO A DECREASE IN THE OSCILLATION RATE OF ONE OF SAID SUPPORT ARMS FOR ESTABLISHING COMMUNICATION OF SAID CYLINDER HEAD AND ROD PORTIONS, ASSOCIATED WITH THE OTHER OF SAID ARMS, WITH SAID PUMPING AND RETURNING PORTIONS OF SAID CIRCUIT. 